Locks of this type are used in exterior doors or apartment entry doors, wherein in the most used embodiment they are inserted as mortise locks into a lock receptacle of the door leaf and are held in the door leaf by means of a plate or the like on the front side. After attaching this mortise lock to the door, the door latch or latches and a lock cylinder are also installed. In the case of an exterior door, a door latch is normally only located on the inside, while a so-called knob, i.e. a non-actuatable handle is installed opposite it on the outside. The latch bolt can be retracted with the aid of the rotatable door latch. If the bolt is in its unlocked position, the door can be opened when the latch bolt is also retracted If no door latch has been attached on the outside, the door can only be opened from the outside with the aid of a key, by means of which the latch bolt can also be retracted. Furthermore, the bolt can be locked as well as unlocked with the aid of key from the outside as well as from the inside.
Locks are also known which are not only locked with respect to the solid frame in the area of the lock or the case of the lock, but also above and/or below the actual lock or the case of the lock, with the aid of additional locking devices. These locking devices provided in additional lock cases must be capable of being actuated simultaneously with the bolt, i.e. brought into an effective position or returned from this position into an ineffective position. Locks are furthermore known wherein the bolt can be brought into an effective position or out of it into a release position by means of a rotatable door latch, wherein of course the latch is also used here for actuating the latch bolt. Locks of this type are available both with and without additional locking devices, at least along the lock side of the door.
An additional lock case is known from German Patent Publication DE 35 03 466 A1, which can be driven by the main lock via a drive rod. This main lock can be embodied in accordance with European Patent Publication EP 0 575 701 A1, for example. In a locking device of this type the bolt is locked and unlocked by means of the lock cylinder. However, it has been shown to be disadvantageous that when opening the door, for example by actuating the door latch, not only the latch bolt but also the bolt of the additional lock case is actuated and displaced into the unlocked position, so that the door can be opened. It is therefore not possible to prevent premature opening of the door, for example by small children, so that uninvited persons have direct access.